Plate blasting machine



Oct. 7, 1952 w. 1. GLADFELTER ET AL 2,612,731

' PLATE BLASTING MACHINE Filed Oct. 9, 1950 4 Sheets-Sheet l Oct. 7, 1952 w. 1. GLADFELTER ErAL 2,612,731

' PLATE BLASTING MACHINE Filed Oct. 9, 1950 4 Sheets-Sheet 2 I JNVENTORS. [17.1- Eladfelzer H.B.H%E'H Oct. 7, 1952 I w. l. GLADFELTER ET AL 2,512,731

PLATE BLASTING MACHINE Filed Oct. 9, 1950 4 Sheets-Sheet s A77 RMK I Patented Oct. 7, 1952 PLATE BLASTING ACHINE Wiltie I. Gladfelter and Robert B. Huyett, Illagers town, Md., assignors to Pangborn Corporation, Hagerstown, Md a corporation of Maryland Application Qctobcr 9, 1950, Serial No. 189,209

8- Claims.

The present invention relates to machines and methods for abrasive blasting ofmetal plates, particularly for blasting new or used metal lithographic plates for the purpose of giving them a grained surface suitable for properly holding the usual image defining coatings.

Among the objects of the presentinvention is the provision of a novel type of plate graining machine and method by means of which lithographic plates are given an improved grain that is more effective for lithographic purposes.

Further objects of the present invention include the provision of an automatic type of plate blasting machine in which the plates-to be blasted do not have to beindividually clamped in place and do not have to be unclamped; butcan be fed through with a minimum of handling and labor.

The above as well as other objects of the present invention will be better understood from the following description of several of its exemplifications, reference being made to the appended drawings wherein:

Fig. 1 is a-sectional side view of one formof automatic plate blasting machine exemplifying the invention;

Fig. 2 is a fragmentary side view of a portion of the plate driving mechanism of the machine of Fig. 1; r y. r

Fig; 3 is a plan view of the construction of Fig. l; I

Fig. 4 is a detail side view of a portion of the nozzle carriage locking mechanism of the construction of Fig. 1; and

Fig; 5 is a front view of the construction of Fig. 1.

According to the present invention a lithographic plate is arranged to be held in curved shape so as to presenta concave surface and an abrasive stream is directed against theconcave surface to grain The plate may be automatically moved along a travel path including'the blasting zone by a supporting structure which automatically engages the plate'without requiring a clamping operation, and advances the plate in steps, an abradant stream being directed between steps along a swath transversely of the plate stepping movement so that swath by swath one entire plate surface becomes grained.

" In the machine shown in Figs. 1 to 5 inclusive, a housing i0 supported on legs l2 includes a loadi'ng apron It a top cover-l6 having a depending front flange l8 and a rear wall the upper portion 22 of which is hinged as" indicated at 26. Side walls 25 complete the upper portion of the housing enclosure. The'lower portions of the housing taper down to a hopper-shaped bottom 26 terminating in an isolating valve 21 and a drain cock 28.

At the rear edge of apron M are rotatably mounted a set of spaced gripping rollers 30, 3|, 32, 33, each cooperating with a closely engaging roller 40, ll, 62 and 43 respectively. These pairs of rollers are positioned so that their nips define a travel path through which the rollers move a metal sheet such as the lithographic plate 35. To assist in guiding the sheet through the path which is curved around a transverse axis, fixed guide strips 38, 44 and 46 may be mounted across the housing as shown. The first pair of rollers I 30,. 43 is mounted in exposed position between the end of apron l4- and the flange l8, so that a sheet can be readily moved into their nip by merely being placed on the apron and slid toward these rollers.

Rollers 30, 3!, 32 and 33, are shown ashaving rubber surfaces held on shafts 50, 5|, 52 and 53 respectively, and each of these shafts carries a gear 60, 3!, 62 and 63 on one end.v These gears areall intermeshed as by the idler gears 56, 58 so that all the rollers are actuated by shaft 53. This shaft 53 also carries a ratchet wheel 66 which cooperates with a ratchet dog 68 connected for to-and-fro movement by an air cylinder 10 to rotate the ratchet wheel one step with each to-and-fro cycle of the dog 68.

As shown therair cylinder 10 has an expansible chamber 12 connected to a source of air under pressure indicated by the line 14. One wall of this chamber '12 is formed by a piston 16 which may carry a sealing member such as a leather gasket l8 and is fixed to a guide shaft which projects from the cylinder, and carries a pivot fitting 82 to which the dog 68 is pivoted as shown by the pivot 84. The fitting 82 may be secured to the shaft as by the taperedpin shown at 86. A spring 88 rests against the internal surface of cylinder 10 and urges the piston in the direction I that compresses the chamber 12. To keep the dog'ea properly aligned, an aligning screw 90 is adjustably held as by a lock nut 92 so that its tip projects into the cylinder bore and engages in an elongated groove 94 provided in the side of It will accordingly be seen that a to escape from chamber 72, the piston will be car- .taining any abrasive. -n1ay1be used to:separate'ly..supply this nozzle.

outwardly extending semi-cylindrical :ca-m I46. -Secured-at each side of the housing ;for cooperation with the cam I46, are look fittings I48-which have upwardly facing scant-cylinried back to the position shown by spring 88 and in this return movement the dog pivots around pin 84 and slides over the teeth of ratchet wheel 66 so that this wheel is not moved. If desired the conventional type of holding catches (not shown) may be fitted against the teeth of ratchet wheel 66, or of any of the other gears, to assure that there will be enough resistance against counterclockwise rotation of this wheel for the dog 68 to pivot and slide over the wheel without rotating it.

Shaft 53 is shown as also carryingasprocket 96 around which a chain 98 is fitted for driving a belt sprocket I suitably mounted for, rotation on a shaft I02. As more clearly shown in Figs. 1

and 3 shaft I02 extends within the housing and cooperates with a corresponding external shaft I04 by means of a set of flexible belts I06 suitably driven as by pulleys I08 fixed to the respective shafts. A tension adjusting mechanism IIO shown as provided forassuring that thebelts are suitably driven. ,Above .the .beltsthe rear wall 20 is slotted as indicated at I I2 so thatmetal sheets deposited onthe upper. run .of the-belts is automatically conveyed .out of thehousing. to ,a

. position where the adyancingpcrtions .of .the

sheets can be withdrawn manually or automatically.

-Ihe forward face .of housinglfl is provided with a blastprojectingassembly.for direct ng a blasting.stream against a concave portion of sheet '35.

.As-shown moreclearly in Figs. l and 5,the.blastinga'ssemblyincludes adoor ,I I4 extending across .the. ,width of thehousingI'fl and pivoted .at its .upperportion on. hinge pin I16, as by means of transversely. slidablewith respect to, the housing I0. Through-a suitable boss I26 in the carriage, one ormore blasting conduits 'I 28 are fitted. "Out- ,.side .of the housing these conduits are' connected .to' a source of ;fluid under; pressure-while internally of the housing the conduits, leadtoone-or ,more blasting vnozzles 1-34. Il'l' the form' of the "invention shown in the-figures eachblast-ing nozzle is the so-called suctiontype in which the discharge of a streampf compressed fluid-causes an abrasive mixture to be suckedi-n-through a secondary feed line I36 so that the abrasive-particles are violently'projected by the nozzle along with the-fluid. 'such a-nozzleis described in U. S.-Patent No.

One very effective construction for 2,369,516 granted February 13, 1945. The abrasive stream is preferably a mixture of-- finely divided grit particlessuch-as sand, in a liquidsucli as "water. -In Fig. l the blasting nozzle assembly is shown as. also includinganauxiliary nozzle I30 which projects a stream: oiwashing fluid not.con-

One of the conduits: I28

. Eorreleasably holding: the; complete door assembly; II4 inplace itis provided at its lowerportions ,with a locking mechanism shown as includ- ;ing atransverse shaft I 22 journa led iii-supports I44 fixed. to; the door-and having on each end. an locking I42 for rotating the rod-about 90 degrees in the journalsupports I44. As shown more clearly. in

away from groove Fig. 4 the semi-cylindrical surfaces of members I46 and I50 are so related that when rod I42 is in the extreme clockwise position shown in this figure, it is impossible for the door-carrying cam I46 to pivot around hinge pin I I6. However upon rotation of rod I42 in a counterclockwise direction, thesemi-cylindrical cam I46 will be turned I50. so *that the downward movement of the-door-wlth the camaround hinge pin I I6 can take place. To bring the door into its ,closed position, it is only necessary to move handle .I52 to its, counterclockwise or lower limit, and -then swing the door into the position shown in Fig. 1 afterwhich handle I52 is returned. to the locking position shown in Fig. 4.

Carriage I24 ,has at its upper edge laterally projecting ears I54 to which are secured the ends of theslurry in the. hopper .26.

of a driving chain I56 held by laterally disposed sprockets (Fig. 5). One of these sprockets is shown as driven through gears I60, I62 actuated .by. means of a driving-motor I64 connected as by adjustably held belt' 166 with a speed reducer I68 which drives gear I'62 through a reversing unit door H4 and pivotally carries a control arm I18 the tip of which is fitted between collars I80, I82

fixed to a transversely slidable-shaft I84 held by support-rings I86 alsofastened to the door. A pair of limit'blocksI88; I adjustably held on the shaft I84 as byset -screws, not-shown, are

arranged to project in the path of an operating nose I92,--which is conveniently formed integral -with thecarriage boss- I'26. By adjusting blocks a 188, I90 to positions along shaft 184 corresponding approximately to'the span occupied bya sheet 35 to be grained, the nozzletravel. can be .correspondi-ngly limited. I Rotation: of motor 164 will cause the carriage I24 to move in-one direction until it engages one of the blocks 188,490 and then carry-the engaged blockand shaft I84 along ..with it'fora suflicient distance to move control arm I18 by the amount required to:-trip.- switch (I -16. 'Acable 1,94 .connecred'from switch I16 to a dualasoleno'id I96 is. thereby, arranged to ashiftia supply of compressed air from line I98. through one of. the lines I891to the dual. air cylinder I14 to effect movement of reversing arm I12xand thereby reverse .the, rotation. of::driven sprocket -.I'58. The carriage istherebycaused to return in the opposite direction until nose I92 engages the opposite block-of the, set I88, I 90-and then returns shaft I84 in the opposite direction to trip control --arm' I18 back ,to' the original position. Continuous :to-anddro carriage -movement is thereby automatically ;obtained.

.In. the, lowerportion of hopper 26 a, slurry: I40 of; abrasive particles and liquid is ,kept to supply theabrasive mixture to nozzle suctionlinexl36.

.'I 11'e;slurrywis-kept agitated during blasting by a circulation system shown as including .a rotary pump 204- having an outlet line 202 connected to thebottom of thehopper and an inlet line 200 opening in the hopper at a level above the bottom -andgenerally above that of which most;of the abrasive particles settle. Thepump 204 is shown as driven by velectriccmotor .206 and keeps the slurry sufiiciently agitated so that the abrasive particles do not pack'down-andare easily-sucked .up into the blasting nozzle. An overflow; linej208 is shown .as-provided for:fixing the upper level Inasmuch .as washing nozzle I38 introduces. liquid which-runs down into the hopper, the overflow will automatically prevent the accumulation of too much liquid in the slurry. The agitation by pump 204 is preferably arranged so that the desired abrasive particles in the slurry will settle sufficiently far that they are not appreciably carried out through overflow '208, while finer particles such as fragmented abrasive and other debris removed from the plate 35 being blasted, will remain in appreciable proportion in the upper layers of slurry I40 and will tend to be washed out with overflowing liquid.

During the blasting large clouds of finelydivided particles of abrasive, debris, and liquid are formed in the housing I 0. To keep these materials from coming out of the housing into the surrounding space and inconveniencing operators stationed nearby, the housing is provided with a suction conduit 2I0. This conduit is connected to the suction side of a blower which is energized whenever blasting is effected. The suction is sufficient to draw in air from around the housing through all the crevices and gaps in the housing Walls, doors, sheet intake and outlet slots, etc. It will accordingly be unnecessary to seal any of these openings.

To simplify the operation of the above machine the compressed air used to operate cylinders '10 and I14 is also arranged to be the projecting fluid connected through conduits I28 to the blasting nozzle I34. As shown in Fig. 3 an air supplyline 2I2 which may include a filter 2M is connected through regulating valve ZIE to solenoid line I98 while another regulating valve 2 It connects line 2 I2 with the driving cylinder line I4. A solenoid valve 2I8 in the last line connection is linked as by cable 220 with the switch I16 so that the solenoid is momentarily actuated with each movement of control arm I18 to permit the compressed air to momentarily operate air cylinder I0. Another branch 222 of the air intake line 2I2 can be directly connected by means of some of the conduits I28 to one or more blasting nozzle I34. If desired, the blasting line may have an additional solenoid control valve connected for operation simultaneously with motor I64 sothat whenever blasting is initiated the driving motor will start carriage traverse ,mocement and prevent gouging of a plate by stationary blasting streams directed at only a portion of the plate.

A feature of the invention is the abrasive blasting of the plate surface while it is in concavely curved condition It has been discovered that this greatly reduces the peening eifect of the blasted particles against the surface, to not only improve the characteristics of the surface with respect to its ability to suitably hold the lithographic coatings normally used to define image areas, but in addition reduces the curvature that always results when blastinga flat or convex surface. This curvature is undesirable and is apparently due to the small amount of expansion which a peened surface undergoes. Such expansion causes the peened surface to be larger than the opposite surface of a treated sheet, and the sheet automatically assumes a somewhat cylindrical curvature with the larger surfaoeon the outside of the cylinder. This is a stable configuration for such an article inasmuch as the curved external surface of the cylinder has a somewhat larger radius of curvature and can therefor accommodate the extra amount of surface present. In practice it is often found necessary to reduce this curvature by bending a sheet in the opposite direction so that the untreated surface is convex andstretches somewhat. This is however, a vioany kind are needed when lent treatment and shortens the life of the plate which normally can be used many times over by repeated regraining, for preparing separate lithographic printing members. A blasting concavity having a curvature radius not greater than one foot and preperably larger than four inches, is very effective.

An additional featureof the machine of the invention is the fact that it will handle and successfully blast plates of any size so long as these plates can be received within the transverse dimension of the'housing. Furthermore no adjustments of I the sizeo'f the treated plates is changed. It may however be desirable to improve the blasting efiiciency of the machine by restricting the td-and-fro travel of the nozzle carriage when plates of relatively narrow widths are being treated. This is conveniently done by merely adjusting the positions of blocks I88, I

be done at any time even and the adjustment can after part of the narrow plate has been blasted.

- In addition to the above no special manipulation is required to fix or clampa plate in the ma chine or to, unclamp the plate for removal from the machine. A plate to be treated is merely fed in until its leading edge is engaged in the nip be-' tween rollers 30, 40, after which the machine automatically feeds the entire plate through, grains it, washes it and delivers it in finishedcon' dition at the discharge end of belts I08. "If desired, an additional conveyor can'be provided for receiving the plates as they roll off belts I06 and deliver them to any. suitable location. I

The specific details of reversing unit I10 as well as of the speed reducer 58 form no part of the present invention and any suitable'types of these well-known mechanisms can be used.

The rollers 40, 4|, resilient rubber surfaces, as shown in the drawings, although only one resilient roll surface is all that is needed at any one nip. If desired, none of the roll surfaces need be resilient in which case it is desirable to have one of each pair of rollers resiliently mounted in its bearings, to assure that the individual plates are suitably gripped and fed through the machine.

In place of the geared interconnections between the driving rollers, a sprocket and chain combination can be used with a single chain driving all the driving rollers as well as the sprocket I00. The chain adjusting idler lBI shown in Fig. 2 can then be relocated and additional idlers supplied if necessary to securely hold the chain engaged with various driving sprockets. Friction type drives such as pulley and belt combination are not as desirable in view of the plate gouging that can take place should the drive slip.

The suction arrangement described above-for reducing the escape of dust, is preferably equipped with a filter or fume arresting mechanism so thatthe withdrawn air can have its suspended contaminants removed after which the purified air can be discharged at any convenient location. Highly effective filter mechanisms are shown in the copending Gladfelter and Garver patent applications Serial No; 114,844, filed September 9, 1949, now Patent No. 2,576,008, granted November 20, 1951; and Serial No. 189,210, filed October 9,. 1950.

,As explained in connection with the first of these copending applications, the hopper isolat ing valve 21 is closed before the machine is shut rupted. This keeps the abrasive particles from 42 and 03 may also have settling in any appreciable quantity in the. small diameter: circulation passageways where they could easily prevent the, resumption of. circulation'. In addition the drain valve 28 can be opened after valve 21 is closed, permitting the rapidly clearing liquid at the pump intake in: the hopper, to flush through the circulation line and wash out substantially all particles before the circulation pump is stopped. Should the slurry circulation passageways inadvertently become blocked, they are most readily cleared by operating the pump with isolating valve 21 closed and drainvalve 28 open. After clearing, the valve 28 is closed and valve 21 opened and slurry agitation will invariably begin regardless of how much settling has taken place in the hopper.

With the above type of machine a blasting air pressure of about 80 pounds per square inch with finely divided sand of about 150 to 250 mesh is highly satisfactory for graining zinc, stainless steel, copper or aluminum plates. Other gases, such as carbon dioxide or steam, may however be used in place of air and other abrasives such as metal powder, carborundum, emery, or glass powder, etc., may be used in place of sand.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope hereof, it is to be understood that the invention is not limited to the specific embodiments hereof, except as defined in the appended claims.

What is claimed is:

1. In an automatic lithographic plate graining apparatus for automatically receiving such plates, automatically graining them and automatically discharging the grained plates; supporting structure for receiving an incoming plate; advancing and guiding mechanism connected with the supporting structure for energization to carry a received plate. in a. predetermined Work path along atleast part of. which the plate is curved; blasting elements connected with the advancing and guiding. mechanism for jetting an abrasive stream toward said. part of the work path in a direction that causes particles of the stream to strike and grain-the concave portion of the curved plate; said advancing. and

guiding mechanism being connected for moving a received plate in small steps along the work path direction, the blasting elementsv are. connected for graining only a portion, of the plates width transversely of the work path direction,

the advancing and guiding: mechanism is connected to the blasting elements for carrying these elements to and fro across the work path between advancing steps and also includes dis-- charge elements connected for automatically carrying the plate out fromsaid part of the work path.

2. The combination as defined by claim 1 in which the advancing and guiding mechanism includes a plurality of closely spaced pairs of grip feed rollers positioned with their nips. defining.

said curved work path. I

3. In an automatic lithographic plate graining.

machine a set of horizontally extending rollers.

for receiving the fiat surface of a lithographic plate; to be grained, said rollers being positioned for energization to grip the received plate and advance it in a work path that curves vertically toconcavely bend one surface of the plate around an. axis directed transversely of the work path;

nozzle structure connected to project a stream of abrasive particles and water against a portionof the concavely bent plate surface to grain that portion of the surface; energizing mechanism connected to carry the nozzle structure to and fro transversely across the work path to grain a transverse swath across the concavely bent plate section, said energizing mechanism being connected for actuating the rollers to advance the i plate along the work path by approximately the longitudinal extent of the swath after each complete traverse of the nozzle structure, for uniformly graining the entire plate, and to discharge the plate after the graining is completed.

4. The combination as defined by claim 3 and further including a fixed support alongside the rollers at the beginning of the work path, said fixed support providing a surface for holding an incoming plate before it is completely entered i into the work path.

5. The combination as defined by claim 3 in which the nozzle structure also includes a washing nozzle for automatically washing the grained plate surface.

6-. The combination as defined by claim 3 in which fixed guide members are positioned alongside the work path to help guide the advancing plate along the work path curve and to support the plate against the deflecting force of the impinging abrasive stream.

7. In an automatic lithographic plate graining machine a set of horizontally extending rollers forreceiving the flat surface of a lithographic plate to be grained, said rollers being positioned for energization to grip the received plate and advance it in a work path; nozzle structure connected to project a stream of sand and water against a portionof the plate surface to grain that. portion of the surface; energizing mechanism connected to carry the nozzle structure to and fro transversely across the workpath to grain a transverse swath across the plate section, said energizing mechanism being connected for actuating. the rollers. to advance the plate along the work path by approximately the longitudinal extent of the swath after each com.- plete. traverse. of. the nozzle structure, for uniformly graining the entire. plate, and to discharge the plate after the graining is completed.

8. The combination. as defined by claim 7 in which the energizing mechanism includes trip members connected to reverse the transverse nozzle. structure movement and to also cause the grip-rollers to go through a plate advancing step,

L and the trip members are adjustable transversely REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Zahn Nov. 28', 1950 

